totm nov 2023 SpaceX Discussion Thread

[mikegarrison]

Also,  making 1000 Starships a year?

Airbus makes 45 A320s a month, which is a little more than 500 per year. Musk thinks the demand for Starships is going to be 2x higher than the demand for A320s?

[Deddly]

12 minutes ago, mikegarrison said:

Musk thinks the demand for Starships is going to be 2x higher than the demand for A320s?

"Aspirationally" 

 

EDIT: In seriousness, I think that's Elon's calculations of what is needed in order to build his city on Mars, which he believes must be done to save humanity. I would gather that he understands that nobody else is realistically going to plan to do it, so he will assume it needs to be done within his lifetime. So it's "do or die", in the way he views things.

Edited June 24 by Deddly

[tater]

1 hour ago, mikegarrison said:

Also,  making 1000 Starships a year?

Airbus makes 45 A320s a month, which is a little more than 500 per year. Musk thinks the demand for Starships is going to be 2x higher than the demand for A320s?

"Demand?"

This is operating under the assumption that Starship (or SpaceX for that matter) exists and/or creates products to serve a need in the marketplace. The marketplace is incidental to their goals, or is seen as a side quest to generate funding for their goals—the market is not the goal.

1000 a year is to build a self-sufficient city on Mars.

Do I personally think such a goal makes sense? Um, no. Doesn't matter what I think or you think, though, it matters what Musk and his company thinks—they want to build a city on Mars.

[cubinator]

1 hour ago, Deddly said:

EDIT: In seriousness, I think that's Elon's calculations of what is needed in order to build his city on Mars, which he believes must be done to save humanity. I would gather that he understands that nobody else is realistically going to plan to do it, so he will assume it needs to be done within his lifetime. So it's "do or die", in the way he views things.

That's definitely where he's getting that enormous number. I think he could stand to calm down just a little, as far as the timescale for humanity destroying itself. I applaud the initiative toward making some progress, though.

[RCgothic]

There's "never done before" and there's "never done before in a rocket engine".

For whatever reason there's never been a good enough motive for someone to try and integrate cooling of secondary systems (because regenerative cooling of combustion chambers and nozzles have been implemented since forever) before. 

Maybe a rocket needs to have a particular mass of fire suppression, number of engines, or level of reusability before advanced integration of instrument lines and wiring inside housings and elimination of flanges makes sense. 

In my own work I'm bringing together a lot of different things that are fairly common elsewhere but nevertheless equal "never done before in a power plant".

The main reason for us at least seems to be that when production of a thing is at a fairly steady rate, the people building power plants go on to build new power plants the same as they've always done, and train their replacements to do what they've always done. 

When demand for a thing exceeds the resource pool, people with different experiences need to get brought in from other sectors and the combination of experiences often unlocks doing things differently from then on.

Edited June 25 by RCgothic

[Nuke]

5 hours ago, tater said:

The tours are fine (vs his other, long form content) in terms of length—just needs to leverage the opportunity.

i watched this one, it was interesting. but i generally dont unless its something im really interested in.

[tater]

33 minutes ago, Nuke said:

i watched this one, it was interesting. but i generally dont unless its something im really interested in.

His deep dives are also decent, honestly. The one about every Soviet/Russian engine, for example. It's just a bit much for me from a watching standpoint, I can listen to four 5-6 hour Hardcore History episodes, but I'd rather see text for stuff like a history of Soviet rocket engines than watch a 1 hour video with the same content.

ObSpaceX:

Tomorrow is FH!

[tater]

 

 

[Flavio hc16]

4 hours ago, RCgothic said:

. 

When demand for a thing exceeds the resource pool, people with different experiences need to get brought in from other sectors and the combination of experiences often unlocks doing things differently from then on.

"Necessity is the mother of all inventions"

[Exoscientist]

18 hours ago, Elthy said:

 

This comment gives a tl:dr for the video. I think, havent watched it myself

• If you're going to the moon, you don't need an orbital depot.

 Can you give the context where he said this? The Starship HLS for Artemis plan requires multiple refuelings. Does he mean a Starship HLS in orbit would itself be the depot?

  Bob Clark

[RCgothic]

34 minutes ago, Exoscientist said:

• If you're going to the moon, you don't need an orbital depot.

 Can you give the context where he said this? The Starship HLS for Artemis plan requires multiple refuelings. Does he mean a Starship HLS in orbit would itself be the depot?

  Bob Clark

He followed up by saying that there's no great rush to refuel HLS in orbit, it can be done with sequential tanker flights and the boil-off won't be too bad. Propellant transfer is just docking, and docking to other starships is easy - much easier than docking to the ISS which they do regularly.

Edited June 25 by RCgothic

[Exoscientist]

On 6/24/2024 at 7:36 AM, Elthy said:

 

This comment gives a tl:dr for the video. I think, havent watched it myself

 

Musk: "[The hot-gas roll thrusters] got clogged with ice. We're not sure how....The location that we're tapping off the engine [to pressurize the LOX tank] is not pure O2. It's got a little bit of water ice... It's Ox-rich gas". Tim Dodd:" So it's incoming off the turbine side?" Musk "Yea. It's got burnt fuel". Dodd: "Wouldn't it have a little bit of C02 in it too then?" Musk: "Yea....We've improved the ice strainers [ice catchers]. We've improved the valves. Something I think we'll do in the future is move to --for critical valves -- series parallel valves. So any one valve failure ... does not take out the ship's ability to orient itself correctly." Dodd: "Are you avoiding doing a more traditional heat exchanger?... I've never heard of an engine using already combusted ...gas... off the pre-burner." Musk: "Yea...We're pressuring the fuel side with gaseous fuel, and the ox side with mostly gaseous oxygen...It affects our max power, especially on the fuel side.... If we turned off autogenous pressurization on the fuel side, we'd actually be able to get more power out of the fuel pump." Dodd: "[Is ice build up what caused the booster shutdown on IFT-3?]" Musk: "Yea, well, we didn't have enough pressure to start the engines...The full answer is quite complicated."

 

  In that Everyday Astronaut  video about 27 minutes in Elon  talks about the autogenous pressurization system:

 

 This is a system that instead of using helium to pressurize the propellant tanks, heats a portion of the propellant to provide the pressurization. But surprisingly rather than using heat exchangers to heat the propellant, the exhaust directly from the pre-burners is used to warm the propellants. Tim Dodd was surprised it was done this way because other times it was done, heat exchangers were used. 

 This appears to be the cause of the recurring problems of clogging of the propellant intakes to the engines they’ve been seeing due to ice developing, since the combustion products include water or CO2 which freeze when contacting the cryogenic propellants.

 I say again SpaceX is desperately in need of a true  Chief Engineer, not someone who dabbles in the field. Can you imagine for example an AI company having as its Chief Technology officer someone who just dabbles in the field of artificial intelligence? Remember, this is not the CEO position here, who might be just a competent manager, this is the person who needs to have a firm understanding and knowledge of all the interconnected technology going on at the company.

 A true Chief Engineer with decades of experience in the SpaceX industry would have known beforehand that using  directly the exhaust products fed into the propellant tanks is a bad idea. 

  Bob Clark

Edited June 25 by Exoscientist

[Terwin]

3 minutes ago, Exoscientist said:

 A true Chief Engineer with decades of experience in the SpaceX industry would have known beforehand that using  directly the exhaust products fed into the propellant tanks is a bad idea. 

  Bob Clark

You know some other bad ideas:

* high pressure combustion  

* transporting large tanks of cryogenics 

* large tanks of fuel and oxidizer close together

* lighting or re-lighting rocket engines in flight

 

All of these have major down-sides that need to be accounted for and designed around.

But without all of them, we would never get to orbit.

Just because something is a bad idea in isolation does not mean it is unnecessary when trying to achieve a specific goal. 

[mikegarrison]

25 minutes ago, Terwin said:

You know some other bad ideas:

But without all of them, we would never get to orbit.

Somehow forcing the LOX into the turbopumps is necessary. Doing it by pumping "oxygen-rich" exhaust from the turbopump is not necessary. It is a choice.

Do not confuse choices for necessities, or vice versa.

[Terwin]

1 hour ago, mikegarrison said:

Somehow forcing the LOX into the turbopumps is necessary. Doing it by pumping "oxygen-rich" exhaust from the turbopump is not necessary. It is a choice.

Do not confuse choices for necessities, or vice versa.

Using cryogenics is a choice, it is entirely possible to get to orbit using compressed oxidizer and non-cryogenic fuel, but compressed o2 does not seem to be the best choice.

Dumping oxygen rich exhaust into the LOX tank my or may not prove to be the superior choice, but we do know that on previous launches the draw-backs of doing so were not properly accounted for.  Probably because it is something new which may or may not prove to be superior to the old preferred choices once everything has been accounted for.  We also know that the refurbishment requirement of using the standard choice of compressed He for pressurization would preclude the stated design goal of rapid reusability.  Perhaps that design goal is not possible, but until it has been discarded as such, autogenous pressurization is the only viable option, and pumping oxygen rich exhaust into the LOX tank still looks like a lower-mass and lower failure-rate option than adding a heat exchanger.

Just because trying new things also introduces new problems does not mean we should never try anything new.

If there were cargo or passengers, then new failure modes would be a concern, but as the only launch product for these test-launches is data, this is the best time to try out new things that may have new failure modes.

Think of it as 'unlocking new rocket parts by trial and error' or 'exchanging funds for science'

Edited June 25 by Terwin

[tater]

The trades on using heat exchangers instead didn't cut it I thought.

This dropped as well:

 

[mikegarrison]

The second-most obvious problem with dumping water and CO2 into a tank of cryogenic oxygen has *also* been discussed in this thread before, and that is, if Musk truly wants the rocket to be able to be launched again in 30 minutes, exactly what does he plan to do about getting those unwanted byproducts out of the LOx tank before he refills it?

[bigyihsuan]

1 minute ago, mikegarrison said:

exactly what does he plan to do about getting those unwanted byproducts out of the LOx tank before he refills it?

I'd imagine that any byproducts in the tank would either be shot out with the rest of the LOX, and/or drained with leftover LOX when landed.

Though, solid ice is a thing, which can be a problem with the "shoot it out with the rest of the LOX" plan. ...Hmm, does water ice float on LOX?

[darthgently]

10 minutes ago, bigyihsuan said:

I'd imagine that any byproducts in the tank would either be shot out with the rest of the LOX, and/or drained with leftover LOX when landed.

Though, solid ice is a thing, which can be a problem with the "shoot it out with the rest of the LOX" plan. ...Hmm, does water ice float on LOX?

"Float" can become a slippery concept when a booster is flipping, burning, with high  gees in variously changing directions, I'd imagine

[tater]

1 hour ago, mikegarrison said:

The second-most obvious problem with dumping water and CO2 into a tank of cryogenic oxygen has *also* been discussed in this thread before, and that is, if Musk truly wants the rocket to be able to be launched again in 30 minutes, exactly what does he plan to do about getting those unwanted byproducts out of the LOx tank before he refills it?

That's the theoretical turn around, but he also explicitly stated that that rate could not happen because of orbital mechanics—you have to wait for the tanker/ship to fly over again, so limited to a few flights a day per pad.

[darthgently]

3 hours ago, mikegarrison said:

The second-most obvious problem with dumping water and CO2 into a tank of cryogenic oxygen has *also* been discussed in this thread before, and that is, if Musk truly wants the rocket to be able to be launched again in 30 minutes, exactly what does he plan to do about getting those unwanted byproducts out of the LOx tank before he refills it?

Spoiler

 

Edited June 25 by darthgently

[darthgently]

 

 

 

 

[sevenperforce]

5 hours ago, Exoscientist said:

But surprisingly rather than using heat exchangers to heat the propellant, the exhaust directly from the pre-burners is used to warm the propellants. Tim Dodd was surprised it was done this way because other times it was done, heat exchangers were used. This appears to be the cause of the recurring problems of clogging of the propellant intakes to the engines they’ve been seeing due to ice developing, since the combustion products include water or CO2 which freeze when contacting the cryogenic propellants.

So it doesn't have anything to do with engine reliability after all, then?

5 hours ago, Exoscientist said:

 I say again SpaceX is desperately in need of a true  Chief Engineer, not someone who dabbles in the field. A true Chief Engineer with decades of experience in the SpaceX industry would have known beforehand that using  directly the exhaust products fed into the propellant tanks is a bad idea. 

All engineering ideas are bad ideas until they are standard practice.

Your feelings about the term "Chief Engineer" are about as strange as your feelings about the term "full duration".

[Terwin]

1 hour ago, tater said:

That's the theoretical turn around, but he also explicitly stated that that rate could not happen because of orbital mechanics—you have to wait for the tanker/ship to fly over again, so limited to a few flights a day per pad.

At 400km altitude(ISS altitude) it only takes 90 minutes to orbit, so if you have the dV to get to an equatorial orbit with each flight you can fly up to 16 times per day, more if you have a lower orbit or use multiple launch pads. (but tandem launches might be a bit much for now)

[sevenperforce]

If a particular use of language communicates the intended point to 99.9% of the expected audience, then that use of language is working just fine.